Rapid vegetable tanning process



mm w 1,899,422

UNITED sTA-ras PATENT? OFFICE eonnorr men, or. nnrnsn name. ABSIG on. or one-mmrom mu-rran 11mm eonrona'rron nun-rm), or cawnroan, narrrsn nsrma, a com cm-rron mm vnemmnnn TANNING r In Drawing. Application fled August, 1988, Serial Io. -301,887, and in India December 8, 1981.

This invention relates to improved methleather it is essential to wash the hides after ods of tanning cow, ox and bufialo hides. depickling so as to remove as much as possi- In the ordinary vegetable tanning processble of the soluble salts therefrom and render es if strong infusions of the tanmng matenthem soft and uniform throughout their subals were used at the commencement of the stance, although for inferior grades of process they would act too strongly on the leather the washin may be omitted. As an surface of the skin under treatment, hardenexample of a suita 1e plckling solution there mg and contracting it so that the subsequent V may be mentioned an aqueous solution of salt tanning of the interior parts would be 1man sulphuric acid. The depickling solution peded. This isavoidedin the methods ordishould be so chosen as to have noill efiect narily employed by the use at first of very on the hide and must be such as to permit of weak infusions. Inthe case of solo leather the hide being brought to a degree of acidity the tanning process may require from three represented by a hydrogen-ion concentration to twelve months for completion. The time of between about H 3.5 and'pH 5.0;solutions taken intanningis now however oftenshort' of the sodium sa ts of most weak acids and 6 ened by drumming and other p m: of articularly sodium thiosulphate have been agitation, assisted very often by the use of ound to give excellent results, and by means strong extract liquors. of the latter the hides can be brought to. a dening process be nry.

The present inventionhas for its object to I gree of acidity represented by a hydrogen-ion prepare the hides in such astute that they concentration of about .pH 3.6to 3.8. maybe rapidly penetrated by the Hides prepared in the manner previously uors and the t comp eted in a mon mentioned maybe rapidly tanned by any of or less in the case of eavyhides such as sole the methods ordinarily in use, the use of such hides, and in a week or two depleuding upon weak infusions as hitherto employed at the the thickness in the case of lig as cow hides for upper leather, without the *nry and the tanning of the hides if de-. useof drumming or the concentrated extract sired bem startedin the stronger liquors. liquors hitherto employed to shorten the tan- It is desira le to maintain-the hydrogen-ion concentration of the tanning solution, as det hides such commencement of the operation bein .un-

is is efiecte by means of the=present termined with the hydrogen electrode, at

invention according to which the hides, after least until the hides are struck through, be- ]iming and preparation for tanning 1n the or tween the required limits, for example of dinary way, are first subjected to the action about pH 3.5 and pH 5.0,dgpending on the deof an appropriate pickling solution until gree of firmness roquuthe finished they are completely delimed and ickled leather and on the tanning materials--uscd .-in -5.:.v

through, whereafter the pickled hi es are the preparation of the tan liquors.

subjected to the action of a depickling solu- An example of the treatment of solo leathtion until they are epickledand 'brou ht 'er by the improved process according to the to a degree of acidityrepresented by aypresent invention is as follows :-The limed drogen-ion concentration of between about unhaired and fleshed hides prepared in the pH 3.5 and pH 5.0 that they can be acted usual manner are suspended in a pickle conupon by the tanning liquor in a compares sisting of- 80 grams of salt and 7.5 gra ns of tively short time, the hides so treated besulphuric acid per litre of water untihtho in then subjected to treatment with the hides are completely dehmed and are m a desired vegetable tanning liquor of the uiuniform state throughout their substance.

site strength and in such manner as to e ect The hides are then suspended in a 10-15 per their rapid tanning. The depickled hides cent solutlon of SOdlllIIl thlosulphate until may, if desired, be washed before subjectthey are depickled and brought to a degree of ing them to the tanning operation. acidity represented by, a hydrogen-mn con- For the production of the best qualities of centration of between about pH 3.6 and pH 3.8 whereafter they are washed for several hours in running water. They are then ready for tanning. In the case of a liquor prepared from the ollowing material s, babul bark 9 parts, myroba-lans 1 part and wattlebark 1.5 parts, they may be suspended at once in a liquor of 60 degree barkometer strength, and provided the strength is maintained a medium thickness hide will be tanned in about 14 days. The actual tanning process used may be varied through wide limits depending on the tanning materials used and weak liquors may be given if desired, but it is necessary if a well tanned leather is required to increase rapidly the strength of the liquor if the tanning is to'be completed in a month or less. For example the process just 'venmay be varied by introducing the hixiis into a 40 degree barkometer liquor for two days, a 50 degree liquor being given on the third day, and a 60 degree liquor on the 4th or 5th day, the strength of this liquor being maintained until the hides are tanned. As an example of another alternative method of carrying out the actual tanning process, the hides may be treated in an 8 degree barkometer liquor for oneday, a 17 degree liquor being given on the second day, a 22 degree liquor on the third day, a 25 degree liquor on the fourth day, and a 30 degree liquor on the fifth day, whereafter the hides are treated for 6 days in a 40 degree liquor, 6 days-in a 45 degree 1i uor, 6 days in a 50 degree liquor, and one we in a 60 degree liquor. Except for the purposes of loading it is rarely necessary to use 7 a stronger liquor than 60-65 degree barkometer.

' For the softer leathers such as cow upper leathers the pickling, depickling and washing are carried out as previously described with regard to sole leather, except that they take place subsequent to the bating or other processes used norma ly for preparing the hides. The tanning is best carried out using weaker liquors than for sole leather and at the higher pH values. A medium thickness cow hide can be tanned in as little as 8 days or even less bysuspension in a degree liquor for one day, moving itforward daily into stronger liquors and finishing in a 30-40 degree liquor or alternatively the tanning may be started and carried out in a '30 or 40 degree barkometer liquor.

In both the examples given above, for the treatment of sole leather and thesofter leathers. the step of washing the hides after depickling them can if desired be omitted, the hides in such case being taken straight from the depickling .bath of sodium .thiosulphate and subjected to treatment with the tanning liquor. I 7

Other methods of pickling and depickling besides these mentioned can be employed, it being necessary of course to ensure,that the particular pickling and depickling means namely also for used are such that the hides are eventually left in a suitable condition, similar to that resulting from the particular pickling and depickling processes hereinbefore mentioned, to enable them to be rapidly tanned in a satisfactory manner.

It may be mentioned that the present process although it is primarily intended to enable the tanning process to be carried out in a much shorter period of time than was heretofore possible without the use of mechanical agitation and/or extract liquors of a high concentration which have constituted the chief means heretofore employed for shortening the tanning process, may nevertheless, if so desired, be employed in conjunction with one or other or both of the aforesaid means.

What I claim and desire to secure by Letters Patent of the United States is 1. A process for the rapid vegetable tanning of cow, ox and buflalo hides which consists in liming and preparingthe hides for tanning in the ordinary way, ing the hides to the action of a ickling solution until they are completely elimed and pickled through, subjecting the pickled hides then subjectto the action of a depickling solution comprising an aqueous solution of sodium thiosulphate until they are depickledonly to such an extent that the hides are brought to a degree of acidity represented by a hydrogen-ion concentration of between about pH 3.5 and pH 5.0, and only thereafter subjecting the hides to treatment with a vegetable tanning liquor of the requisite strength so as to effect their rapid tanning.

2. A process for the rapid vegetable tan-' ning of cow, ox and bufialo hides which con-, sists in liming and preparing the hides for tanning in the ordinary way, then subjecting the hidesto the action of a icklin solution until they are completely dblimed and pickled through, subjectifig the pickled hides to the action ofa depic mg solution comprising an aqueous solution of sodium thiosulphate until they are depickled only to such an extent that the hides are brought to a degree of acidity represented by a hydrogen-ion concentration of between about pH 3.5 and pH 5.0, removing the hides from the depickling solution and washing them, .and thereafter subjecting the washed depickled hides to treatment with a vegetable tanning liquor of the requisite strength so as to efiect their rapid tanning.

3. A process as in claim 1, in which the pickling solution comprises an aqueous solution of salt and sulphuric acid.

4. A process as in claim 2, in whichthe pickling solution comprises an aqueous solution of salt and sulphuric acid.

5. A process'as in claim 1, in which the pickling solution comprises an aqueous solution of salt and sulphuric acid and in which the tanning liquor is maintained at a. degree of acidity represented by a hydrogen-ion w concentration of between about pH 3.5 and H 5.0 until the hides are struck through.

6. A process as in claim 2, in which the pickling solution comprises an aqueous solution of salt andsulphuric acid and in which the tanning liquor is maintained at a. degree of acidity represented by a hydrogen-ion concentration of between about pH 3.5 and pH 5.0 until the hides are struck throu h.

GORDON PEA E. 

